Tension control for filamentary materials



Feb. 20, 1962 E. J. SAXL 3,022,025

TENSION CONTROL FOR FILAMENTARY MATERIALS Filed Aug. 3, 1959 4 Sheets-Sheet 1 egg, QS 33 a 44 65 Feb. 20, 1962 E. J. SAXL TENSION CONTROL FOR FILAMENTARY MATERIALS 4 Sheets-Sheet 2 Filed Aug. 3, 1959 132121282203 32 mm JISaJGZ,

w o 4 T M E a @v w Wu 6% H w M 4 fl 4% A fl r 4 w 4 W g 7 7 4 4 6 L/ w 8 I L ae Feb. 20, 1962 E. J. SAXL TENSION CONTROL FOR FILAMENTARY MATERIALS 4 Sheets-Sheet 5 Filed Aug. 3, 1959 Invenion- Feb. 20, 1962 E. J. SAXL TENSION CONTROL FOR FILAMENTARY MATERIALS 4 Sheets-Sheet 4 Filed Aug. 3, 1959 United States Patent Office 3,022,025 Patented Feb. 20, 1962 3,022,025 TENSION CONTRQL FOR FILAMEN'IARY MATERIALS Erwin J. Sax], Harvard, Mass, assignor to Tensitron, Inc, Harvard, Mass, a corporation of Massachusetts Filed Aug. 3, 1959, Ser. No. 831,352 8 Claims. (Cl. 242-155) This invention relates to devices for controlling the running tension of yarn, Wire and similar filamentary materials during such operations as knitting, weaving, de-reeling, or winding. This application is a continuation-in-part of the inventors copending application Serial No. 511,202, filed May 26, 1955, now abandoned.

The control of tension of a running filament is of utmost importance in many operations. In the textile field, for example variations in tension of the yarn during the various yarn preparatory operations results in flaws in the cloth, uneven selvages, non-uniform load distribution over the individual components, such as the strands or shrouds of parachutes, cordage and the like, with resulting impairment to shock load strength, and other defects. When synthetic yarns are used, excessive tension, though below the breaking point of the yarn, may result in a permanent deformation which changes the dye absorption and light reflecting characteristics of the yarn. In wire handling operations, for example, in winding coils for precision electrical components, it is essential to maintain correct, uniform tension in order to produce coils of uniform electrical characteristics. Variation in the tension on the wire during winding will result in tighter or looser winding and therefore variation in the number of ampere turns between one coil and another. If the wire is stretched beyond its elastic limit, its diameter is permanently reduced and its ohmic resistance is increased. Such defects, in a lamp or tube filament for example, will produce hot spots and cause the filament to burn out before its normal life or load limit is reached. Control of tension is especially important when winding fine enamelled wire, such as that commonly used for coils in electrical components. Excessive stretching, even though the tension is within the elastic limit of the wire itself, produces crazing, or microscopic cracks, in the insulation which is less elastic than the wire. This condition is likely to cause short circuits in the coil.

Magnetic recording tape is also very sensitive to variations in tension, both in recording and reproducing. In sound reproduction systems, such variations produce distortion. In computing and data handling systems, the accuracy of the equipment is affected by variations in tape tension.

Changes in tension in a running yarn or wire are caused by a number of factors such as variation in speed of the motors which drive the winding or other mechanism, starting and stopping, change in diameter of the winding and unwinding reels as the material is run olf, or the noncircular shape of a core on which the material is being wound, as in winding square or rectangular coils.

The principal object of this invention is to provide a simple and effective device for maintaining substantially constant tension on a running filament under various operating conditions. Another object is to provide a device which may be used on delicate filaments, such as fine synthetic or glass yarns or insulated wires without danger of damage to the material. Still another object is to provide a means of readily adjusting the tension for different requirements. Another object of the invention is to stop the filamentous material quickly when the winding or other machinery is stopped. Other objects, advantages, and novel features of the device will be apparent from the following description.

The device consists, in general, of a drag wheel of low inertia, a braking device for applying varying amounts of drag to the wheel, and a replaceable cover for the wheel made of elastic material and having a groove in which the filament is engaged. The cover preferably has, in the groove, transverse serrations which provide good traction between the wheel and the filament but are yieldable to avoid crimping the filament. The device is preferably provided with a stop mechanism which stops the wheel, when the winding or other machine is stopped, to prevent overrunning.

In the drawings illustrating the invention:

FIG. 1 is a front view, with part of the casing broken away, of preferred form of a tension control device constructed according to the invention;

FIG. 2 is a cross-section taken along line 22 of FIG. 1;

FIG. 3 is a fragmentary cross-section, somewhat enlarged, taken along line 3-3 of FIG. 1;

FIG. 4 is a fragmentary cross-section, somewhat enlar ed, taken along line 44 of FIG. 1;

FIG. 5 is a side view of the tension wheel;

FIG. 6 is a rear elevation of the wheel;

FIG. 7 is a rear view of one form of expendable cover for the wheel;

FIG. 8 is a fragmentary cross-section, somewhat enlarged, taken along line 8--8 of FIG. 7;

FIG. 9 is a side elevation, partly in cross-section, of an alternate form of expendable cover;

FIG. 10 is an electrical schematic diagram of a circuit for energizing the drag magnet;

FIG. 11 is a horizontal, fragmentary cross-section of a modification of the control device, taken in the same general region as FIG. 3;

FIG. 12 is a fragmentary cross-section taken along line 1212 of FIG. 11; and

HG. 13 is an end elevation, on a somewhat reduced scale, of the control device of FIG. 11.

As shown in FIGS. 1 through 4, the various parts of the device are supported on a casing 20 having a front plate 20a and are enclosed at the rear by a cover plate 21. The casing is mounted in any convenient manner, for example by means of a post 22 and clamp block 23 above a bobbin holder 24, containing a bobbin 25 of conventional type from which the yarn, wire or other filamentary material 26 is to be run off overhead.

A dancer arm 27 is pivoted by a pin or shaft 28 to a block 29 secured to the under side of the casing 20. The dancer-arm carries three grooved guide pulleys 3t), 31 and 32, and is normally urged upward by means of a tension spring 33 connected to an adjusting screw 34 mounted on a bracket 35 on the casing. Mounted on the dancer arm is a block 36 to which is attached a flux gate 37 of magnetically permeable material. This gate extends upward into the casing through a slot 38 in the bottom of the casing.

A wheel, generally indicated by the numeral 40, is mounted on a shaft 41 which runs through a bearing 42 in the front wall 20a of the casing. Mounted behind the Wheel is a stationary guard 43. A ring-shaped cover, generally indicated by the numeral 44, is mounted on the wheel. Secured to the shaft 42 behind front Wall 20a is a hollow drum 45, having a rearwardly extending, externally threaded, flange 45a. A tubular drag cup 46 of magnetically permeable material is internally threaded and screwed on to the outside of drum flange 45a. [Drag cup 46 has a radially projecting flange 46a by which the cup can be grasped to turn it to adjust its position axially.

Mounted in the casing in any suitable manner, for example by bolts 59, is a stack of generally U-shaped magnetic laminations 51. A coil 52 is mounted on these laminations and has leads 53 and 54 passing out through the casing. These laminations each have a long upper leg 51a which extends over the top of cup 46' and a shorter lower leg 51b. Another stack of laminations 55 is connected to legs 51b by means of non-magnetic bridging plates 56 and 57, and extend around the lower part of cup .46. -Laminations 55 and-the leg parts 51a of laminations 51 are joined together on each side of cup 46 by magnetic bridging pieces 58 and 59, so that the whole assembly forms a magnetic core having a generally circular gap 60 in which cup 46 revolves, and a straight gap 61 in which gate 37 moves. up and down. A stack of circular laminations 62 is mounted inside cup 46. These laminations are supported by bolting them to an extension of plate 57. It is understood that the clearance between cup 46 and the inner and outer sets of laminations is somewhat exaggerated in the drawings for clarity. It is desirable to make the clearance as small as practicable in order to obtain maximum efiiciency of the magnetic circuit.

A hinge leaf 63 is secured to the leg part 51a of laminations 51 and is hinged to an armature 64 made of magnetic material. The armature carries a yoke 65 which surrounds drum 45. Armature 64 is urged upward by a tension spring 66, and yoke 65 carries a brake shoe 67 which engages drum 45. When coil 52 is energized, the magnetic field of the core assembly draws armature 64 down and disengages the shoe from drum 45.

The wheel 40, shown in detail in FIGS. and 6, is made of light weight plastic or aluminum, and has a forwardly sloping rim 40a, and a number of spaced openings 4011 from which tabs 400 are bent toward the rear, forming with the rim a discontinuous V-shaped peripheral groove 40d. The wheel has a hub 40c and may have radial stifiening ribs 40 The wheel is rigid enough to withstand considerable tension from the wire or yarn passing around it, but is yet of extremely light weight. One form of wheel cover 44, shown in FIGS. 7 and 8, is formed of inner and outer layers 44a and 44b of soft elastomeric materiah'such as rubber. The layers are of contrasting colors so that it will be immediately apparent when the outer layer has worn through and the cover should be replaced. The cover has a pair of hollow flanges 44c and 4444, which fit around rim 40a and tabs 49c, respectively, and define a V-shaped groove 44a. As shown in FIG. 3, the cover has small transverse ribs 44; in the groove. 7

An alternative form of cover 70 is shown in FIG. 9. This cover has the same general shape as that of FIGS. 7' and 8, with hollow flanges 70a and 70b defining a V- shaped groove 700, but is made of a ribbed knit material with the ribs 79d disposed preferably cross-wise, to provide good traction. The cover may be formed by cutting oii a piece of tubular knit material, impregnating it with latex or mild sizing and placing it to dry on a suitably shaped mandrel. The rubber cover is best for wire, and the knit cover for delicate yarns which are very slippery, such as nylon or other synthetics. When using a knit tubular cover, selvages are preferably cross-knit into the knitted tubing from which the covers are made so that individual covers can be cut off without unravelling.

In all cases the cover provides good traction for the filament. The ribs increase the traction but, being made of relatively soft elastic material, do not crimp or damage the filament. This is especially important in the case of fine wire which is likely to become permanently orimped when run over rigid Washboard wheels of conventional type. For use with corrosive filaments or filaments having a corrosive coating, a cover similar to that of FIG. 9 made of fine stainless steel mesh may be employed.

A circuit for'energizing the coil 52 is shown in FIG. 10. A pair of terminals 71, 72 are connected to a power source, which may be AC. or D.C., for example the source for operating the winding or other machine. The circuit includes a switch 73, which may be the start and stop switch of the machine, a variable resistor 74, and a rectifier bridge 75, all connected in series. The output of the rectifier bridge is put through a potentiometer 76 and the coil 52. Resistor 74 provides the range or coarse adjustment, and potentiometer 76-provides fine adjustmeut of the current through coil 52.

The operation of the device is as follows:

The filament 26 is led around the groove in the cover of wheel 45 and around guides 30 and 31, as shown in FIG. 1. These guides hold the filament in contact with the wheel cover around a considerable part of its periphery. The filament is led over guide pulley 32 and from there passed to the Winding or other device. The amount of drag to produce the desired amount oftension on the filament is set by means of resistors 74 and 76 and can also be adjusted by screwing cup 46 in or out along drum 45 so as to change the depth to which the cup enters the gap 60 in the magnet core assembly. Preferably, the final adjustments ot-the tension are made while the machine is running.

Under the running tension, arm 27 is pulled down somewhat and gate 37 is partially out of gap 61. An increase in tension will cause arm 27 to be pulled down further, drawing gate 37 further out of gap 61. This reduces the magnetic field and consequently the drag on cup 46, restoring the tension to normal. If the tension drops below normal, arm 27 rises, causing gate 37 to close more of gap .61, and the magnetic drag and resulting tension are increased. Because of the extremely low inertia of the wheel assembly, the response of the device is practically instantaneous, so that the tension is kept uniform within close limits.

As previously stated, the energizing circuit forcoil 52 preferably includes the starting switch of the machine. Therefore, the coil becomes deenergized whenever the machine is stopped, and the brake mechanism, consisting of armature 64 and yoke 65, goes into operation to stop the wheel. This positive braking action prevents the filament from overrunning and building up slack, which might result in a loose coil on a coil winding machine, for example.

The device can, if desired, be used as a fixed drag device by locking arm27 to the casing in any convenient manner, or simply by running the filament around the wheel and guides 39, 31 only, skipping guide 32. In op erations which do not cause appreciable fluctuations in the running tension of the filament, using thedevice in this manner may be satisfactory.

For some purposes it is desirable to connect a revolution counter fit to shaft 41 to measure the amount of material which is run over the wheel. For example, in Windin coils for eleotricial components it is desirable to maintain accurate control over the number of turns. The counter can be calibrated to indicate the number of tunns. By controlling the tensions, as well as the number of turns, the electrical characten'stics'of coils can be controlled with a high degree of precision.

in the modified formof the device shown in FIG. 11, the Wheel and drag cup assembly are the same as in the form previously described. The magnetic core is made up of a stack of M-shaped laminations 80 having central legs a and short side legs 80b and Silo. Two stacks of laminations 81 and 82 are mounted alongside the ends of legs 8% and "800, respectively, forming gaps 83 and 84. Arm 27 carries angles 85'and36 which extend up through slots 87 and 88 in the casing and form flux gates in gaps 83 and 84. The excitingcoil 89 iswound around legs Sila. This coil is connected in the circuit of FIG. 10 in place of coil 52, and the device operates in essentially the same manner as that previously described, gates 85 and 86 moving up and downto alter the magnetic drag on cup 46 as arm 27 moves in response to variations in tension.

For applications where only a small range of tension adjustment is required, a permanent magnet may be used in place of the electromagnet assembly. Adjustment of the wheel drag is made entirely by changing the position of the drag cup.

The wheel is preferably made as small as feasibly consistant with providing enough surface for the filament to run on to supply the necessary traction without damage to the filament. A wheel of 2 to 2 /2 inches in diameter is suitable for most fine yarns and wires. The drum and cup are made as light as possible so that the whole running assembly has a low inertia. This is important not only to achieve fast response to changes in the magnetic field but also to prevent breakage of delicate filaments in starting.

The entire device is relatively inexpensive. The exendable covers can be replaced at very little cost and are slipped on and ed without dismantling or afiecting the setting of the device. The device is thus practicable for controlling individual thread tension, in multiple station machines, such as multiple coil winders for example.

The term filament is here used in the specification and claims in a general sense and is intended to include multiple as well as single strand yarns, wires, tapes and other filamentous materials. The device may be adapted for tape tension or film tension control simply by Widening the bases of the grooves in the wheel and cover. This will reduce shock tensions on films, tape, and the like, such as occur in the start-and-stop motion of moving picturecameras and projectors as well as in the rapid acceleration and stopping, respectively, of data-handling equipment based upon magnetic recording and locating devices of magnetizable tape and wire. By reducing shock tensions as outlined above, tension peaks can be reduced and the tape thus can be engineered to run safely at lower breaking strength resulting in the safe use of thinner tapes and larger capacity of the tape drums.

What is claimed is:

1. A device, for controlling tension of a running filament, comprising a supporting member, a wheel rotatably mounted on said member and having a peripheral surface adapted to engage said filament, means for maintaining said filament in contact with said surface, a magnetically permeable member attached to and rotatable with said wheel, a magnet mounted on said supporting member and having a first gap and a second gap, said permeable member being rotatable in said first gap and braked by the field of said magnet, a dancer arm mounted on said supporting member and having means engaging said filament, said arm being movable in response to variations in tension of said filament, and a gate of magnetic material mounted on said dancer arm and extending into said second gap and disposed to be moved in and out of said gap by movement of said dancer arm, thereby varying the braking efiect of said magnet on said permeable member.

2. A device as described in claim 1, said permeable member being of generally tubular shape, and said magnet having portions disposed inside and outside said permeable member.

3. A device as described in claim 1, said permeable member being of generally tubular shape and said magnet including a generally rectangular portion disposed to surround said member and a generally cylindrical portion disposed inside said member, and said second gap being disposed in said rectangular portion.

4. A device as described in claim 1, said permeable member being of generally tubular shape, and said magnet having a central leg extending inside said permeable member, and a pair of end legs disposed on opposite sides of said permeable member, said second gap being disposed in one of said end legs, and the other end leg having a third gap, said dancer arm carrying a second gate movable in and out of said third gap.

5. A device, for controlling tension of a running filament, comprising a rotatable Wheel assembly including a wheel, a member having a brake receiving surface, and a magnetically permeable member, said wheel having a peripheral surface adapted to engage said filament, an electromagnet creating a magnetic field in which said permeable member rotates, means for energizing and deenergizing said electromagnet, a movable armature adapted to move toward said magnet when the magnet is energized, means for moving said armature away from said magnet when the magnet is deenergized, and a brake member carried by said magnet and disposed to frictionally engage said brake receiving surface when said magnet is deenergized.

6. A device, for controlling tension of a running filament, comprising a wheel having a peripheral surface adapted to engage said filament, a brake drum and a magnetically permeable member attached to and rotatable with said wheel, an electromagnet adapted to create a magnetic field in which said permeable member rotates, means for energizing and deenergizing said magnet, an armature hinged to said magnet and disposed to be drawn toward said magnet when the magnet is energized, a spring adapted to move said armature away from said magnet when the magnet is deenergized, and a brake member cmied by said armature and adapted to frictionally engage said drum when said armature is moved away from said magnet and to be disengaged from said drum when said armature is drawn toward said magnet.

7. A device for controlling tension of a running filament, comp-rising a supporting member, a wheel rotatably mounted on said member and having a peripheral surface adapted to engage said filament and an axis of rotation, a substantially tubular drag cup of magnetically permeable material disposed concentrically with respect to said wheel, a magnet mounted on said supporting member and having a first gap in which a portion of said cup is disposed, and a second gap, said magnet being disposed in fixed position with respect to said wheel axis, an adjustable connection between said cup and said wheel providing movement of said cup along said axis toward and away from said wheel, whereby the portion of said cup disposed in said first gap can be varied, a dancer arm mounted on said supporting member and having means engaging said filament, said arm being movable in response to variations in tension of said filament, and a gate of magnetic material mounted on said dancer arm and extending into said second gap and disposed to be moved in and out of said second gap by movement of said dancer arm, thereby varying the braking eifect of said magnet on said permeable member.

8. A device as described in claim 7, said connection comprising a drum attached to said wheel and threadably engaged with said cup.

References Cited in the file of this patent UNITED STATES PATENTS 651,219 Wardwell June 5, 1900 2,124,422 Klein et al July 19, 1938 2,73 8,937 Roughsedge Mar. 20, 1956 2,768,796 Levine Oct. 30, 1956 FOREIGN PATENTS 1,135,176 France Dec. 10, 1956 1,176,203 France NOV. 24, 1958 

